1. Field of the Invention
This invention relates to a tire building apparatus, and more particularly to tire building apparatus laminating uncured materials such as a belt material, a tread rubber material and the like onto a green case for a radial ply tire and capable of particularly positioning an accurate centering of a green case transferred from another building apparatus.
2. Description of Related Art
A tire building apparatus conducting the building at two stage is as follows.
That is, a tire building apparatus of a first stage laminates an innerliner rubber material, a radial carcass ply material, a bead core material and rubber materials surrounding them (a bead filler rubber or a stiffener rubber, and a chafer rubber) and, if necessary, a sidewall rubber material together to form a cylindrical green case. In this case, all materials are uncured materials and so forth on.
Then, outlines of two conventional tire building apparatuses 50, 50A of a second stage are described with reference to FIGS. 5 and 6, wherein such apparatuses are shown as a right-half section of their main part in FIGS. 5 and 6, respectively. Each of the building apparatuses 50, 50A comprises a pair of grasping members 52, 53 airtightly grasping an expandable cylindrical bladder 51, and a group of many segments 54 each slidably engaging with the outer grasping member 53. They form a building drum.
And also, each of the building apparatuses 50, 55A comprises a pair of ring-shaped pistons 55, 55A engaging with the group of these segments 54 and enlarging each segment 54 by its inward movement along a rotating axial line X, and a pair of opposed double-wall cylinders 56 slidably housing the pistons 55, 55A therein. Each of the segments 54 is provided on a side of an outer periphery with a flange 54f located inward in the direction of the rotating axis X.
In the apparatuses 50, 50A shown in FIGS. 5 and 6, the piston 55, 55A locates at an operating standby position. The cylinder 56 has a space 56S at a back side of the piston 55, 55A. The space 56S is connected to a supply means of a pressurized gas such as pressurized air or the like (not shown) and a vacuum means (not shown). The piston 55, 55A is provided with a slant face 55s, 55As taperingly extending toward an inward top in the direction of the rotating axis. On the other hand, each of the segments 54 has a disc 54d rotatably contacting with the slant face 55s, 55As.
The tire building using the apparatuses 50, 50A will be described simply below. At first, a green case GC is transferred by a ring-shaped grasping device (shown by a phantom line) grasping the green case from its outside to an outer peripheral side of the bladder 51 and subjected to a centering with respect to the group of the segments 54. At a state of holding the green case, the piston 55, 55A is moved inward in the rotating axial direction by supplying the pressurized gas to the space 56S.
The disc 54d rises on the slant face 55s, 55As accompanied with the above movement. Thus, the group of the segments 54 is enlarged in the radial direction, whereby each of the flanges 54f is located inward in the vicinity of each bead portion Bp of the green case GC. In this case, the outer peripheral face 54os of each segment 54 is separated away from the inner face of the bead portion Bp. This is a first stage of enlarging the segments 54.
Thereafter, the group of the segments 54 is moved outward in the direction of the rotating axis X to enlarge the segments in the radial direction and hence widen a width of the building drum, whereby each of the flanges 54f is pushed onto the inside of the bead portion Bp in the green case GC. Then, the group of the segments 54 is further enlarged in the radial direction to push the outer peripheral face 54os of the segment 54 to the inner face of the bead portion Bp, whereby the pair of the bead portions Bp are engaged with the group of the segments 54. This is a final stage of enlarging the segments 54 in the radial direction. As such a state, the green case GC is released from the grasping device 60 and moved into a subsequent building step.
In case of the apparatus 50 shown in FIG. 5, however, even if a pressure of the pressurized gas to be supplied to the space 56S is adjusted by any processes in a gas supplying source, a space required between the outer peripheral face 54os of the segment 54 and the inner face of the bead portion Bp can not be ensured due to the scattering of the adjusted pressure and the scattering of slide resistance of the piston 55 and hence both faces are at a state of contacting with each other. When the width of the building drum is widened at such a state, there is caused a large change in the centering of the green case GC with respect to the building drum through the grasping device 60.
In this connection, the apparatus 50A shown in FIG. 6 has a merit that the change in the centering is made smaller than that in the apparatus 50. That is, the piston 55A of the apparatus 50A has such a structure that the slant face 55As is divided into two slant face portions 55As-1 and 55As-2 and a flat face portion 55Asf is positioned between the slant face portions. Thus, it is intended to control a quantity of each segment 54 enlarged to a given value on the flat face portion 55Asf. Even in this case, however, it can not be avoided to have an influence by the scattering of the adjusted pressure and the scattering of slide resistance of the piston 55, so that it is not ensured to stay the rotatably contacting disc 54d on the flat face portion 55Asf. As a result, there is caused a big change of the centering, which is said to be smaller than that of the apparatus 50 but can not overlook at all.
Such a change of the centering brings about the occurrence of poor uniformity in a tire after an uncured tire is subjected to tire building through vulcanization. This type of the centering change occurs over all tires. Particularly, in case of a tire having a structure that a carcass ply is not arranged in at least a central region of a tread portion, an elongation of a portion not existing the carcass ply in the direction of the rotating axis X becomes large and hence the change of the centering is considerably large, which is a serious problem.
It is, therefore, an object of the invention to provide an apparatus eliminating all of the aforementioned problems, concretely a tire building apparatus capable of accurately and easily holding a centering of a green case transferred to a given position and positioned once to a building drum even if there are existent various scattering factors in the operation of the building apparatus and completely eliminating poor tire uniformity due to the change of the centering.
According to the invention, there is the provision of a tire building apparatus comprising a group of many segments enlarging a size in a radial direction to pushingly lock a bead portion of a green tire, a ring-shaped inner piston engaging with the segments of such a group and moving inward in a direction of an axial line to enlarge the size of each of the segments, a ring-shaped outer piston contacting and engaging with a back face of the inner piston to move the inner piston inward in the direction of the axial line, a cylinder slidably housing the inner piston and the outer piston in its double wall, a pair of gas pressure acting means moving each of the inner piston and outer piston housed in the double wall inward or outward in the direction of the axial line, and a stopper formed in the cylinder for stopping the inward movement of the outer piston at a given position before the completion of the inward movement of the inner piston.
In a preferable embodiment of the invention, the inner piston has a slant face taperingly extending toward its inner top end and contacting and engaging with each of the segments, and the slant face has a mechanism that the size of the segment is enlarged in the radial direction accompanied with the inward movement of the inner piston.
In another preferable embodiment of the invention, the group of segments has a tensile elastic means stretching in the radial direction in the enlargement of the size of the segment and is provided on inner end portion in the radial direction with a wheel rotatably contacting with the slant face of the inner piston.
In the other preferable embodiment of the invention, the inner piston has a first-stage moving stroke corresponding to a moving stroke of the outer piston and a second-stage moving stroke further moving over the moving stroke of the outer piston to conduct the size enlarging operation of each of the segments at two stages.
In a further preferable embodiment of the invention, the group of segments has a push-locking face at a first size-enlarging stage having a clearance of 0.5-1.0 mm to an inner face of the bead portion of the green tire and a push-locking face at a second size-enlarging stage pushingly locking the bead portion of the green tire.
In a still further preferable embodiment of the invention, the gas pressure acting means is provided with a pressurized gas supply device for supplying two kinds of high-pressure and low-pressure gases, and the pressurized gas supply device has means for supplying a low-pressure gas to a back face of the outer piston and means for supplying a high-pressure gas to a back face of the inner piston and a back face of the outer piston, respectively.
In another preferable embodiment of the invention, the cylinder has a gas path communicating to an exterior at a back face size of the inner piston in a waiting position thereof and a gas space located at the back face side of the outer piston in the waiting position, and means for supplying a high-pressure gas is connected to the gas path and a pressurized gas supply device for supplying two kinds of high-pressure and low-pressure gases is connected to the gas space.
In the other preferable embodiment of the invention, the pressurized gas supply device for supplying two kinds of high-pressure and low-pressure gases in the gas pressure acting means comprises a first check valve, a pipe connecting a gas inlet port of the check valve to the gas space and a pipe connecting a gas outlet port of the check valve to the gas path, and the first check valve has a cracking pressure exceeding a pressure of a low-pressure gas but being less than a pressure of a high-pressure gas.
In a further preferable embodiment of the invention, the gas pressure acting means comprises a vacuum means and a directional control valve switching connection to the vacuum means and connection to the gas space in the pressurized gas supply device, and the gas space is communicated with the pressurized gas supply device and the vacuum means through the directional control valve.
In a still further preferable embodiment of the invention, the gas pressure acting means comprises a first check valve and a second check valve arranged in series, and the second check valve is connected at its gas inlet port to a gas outlet port of the first check valve and at its gas outlet port to a gas inlet port of the first check valve, and the second check valve has a cracking pressure exceeding a vacuum pressure but being less than an atmospheric pressure.